In building automation technology, a large percentage of heating ventilation air conditioning (HVAC) sensors have displays to indicate status information. Such status information is generally transmitted to the display, such as a signal indicating that the battery powering a thermostat is near the end of its useful life and needs to be replaced. Similarly, a thermostat unit itself may have a visual indictor, such as a light or LCD display, for displaying the actual temperature, the desired temperature, and the battery condition. These displays have traditionally used liquid crystal display (LCD) technology as other display technologies have been too expensive, until recently.
Displays on conventional HVAC sensors are often difficult to read because of low resolution and low contrast ratios. Some conventional displays or keypads offer only very limited feedback in the form of light emitting diodes (LEDs). Alternatively, some HVAC sensors utilize more flexible and customizable liquid crystal display (LCD) panels. However, LCD panels are expensive to manufacture and typically have a contrast ratio of only about 80. In addition, most LCDs have an off-axis viewing angle limitation of about 45 degrees or less. Additionally, LCD displays are reflective and may only be viewed when sufficient lighting is on them. It should also be noted that LCD displays may be back lit to make them more visible, but due to the nature of LCD's backlighting, the contrast is reduced, making it harder to see. Lastly, the backlighting of an LCD consumes large amounts of power and HVAC sensors are always sensitive to how much power is dissipated under the sensor housing.
Therefore there is a need for improvement in HVAC sensors and in particular the display panels for the HVAC sensor.